Phenotype
Definition
The observable serological result for a blood group system, determined by which antigens are present on the red cell surface. Two people can share the same phenotype but have different underlying genotypes, which limits the precision of phenotype-based deductions.
- Domain
- Blood group serology
- Determines
- Antigens present on the red cell surface
- Relation to genotype
- Same phenotype can arise from different genotypes
- Use
- Paternity and kinship blood typing
Common questions
Why does phenotype ambiguity matter in a paternity dispute?+
Because two unrelated genotypes can produce an identical antigen pattern, a shared phenotype between alleged father and child is supportive but not definitive, which is one reason DNA profiling largely replaced blood-group typing for paternity work.
How is red cell phenotype actually determined in the lab?+
Serologists mix the sample with known antisera and observe agglutination reactions; the pattern of which antisera cause clumping identifies which antigens are present on the cell surface.
Can phenotype change during a person's lifetime?+
Ordinary ABO and Rh phenotypes are stable from birth, but certain disease states, transfusions, or rare acquired conditions can transiently alter antigen expression, which is why fresh, well-documented samples are preferred in casework.
Related terms
- Exclusion
- The categorical conclusion that one or more examined features are clearly inconsistent in a way that cannot be explained by projection angle,...
- Exclusion Probability (PE)
- The proportion of unrelated men in the relevant population who would be excluded as fathers of a child with the observed maternal...
- False Exclusion
- An incorrect serological finding that excludes a true biological parent. Causes include chimerism (two cell populations in one individual), rare antigen variants,...
- Non-Exclusion (Inclusion)
- A finding that the alleged parent's blood group profile is compatible with parentage. Non-exclusion does not prove parentage: it means only that...
- Paternity Index (PI)
- A likelihood ratio that compares the probability of the observed serological profile if the alleged father is the biological father to the...